Last year, state TV told viewers that Russia was the only country capable of turning the United States into "radioactive ash." This week, two pro-Kremlin channels revealed how Moscow's military might go about doing it.

For a few seconds on November 10, evening news programs showed a document with drawings and details of a planned Russian nuclear-capable underwater drone that would be launched from a submarine, dubbed Status-6.

In bland but chilling language, the document said the purpose of the pilotless subs -- still on the drawing board and at least a decade away from any possible production -- would be to "strike important enemy economic facilities in coastal areas." Such attacks, it said, would create "zones of extensive radioactive contamination unfit for military, economic or other activity for a long period of time."

The Kremlin quickly described it as a mistake.

President Vladimir Putin's spokesman, Dmitry Peskov, said that NTV and state-run First Channel had erred by slipping "secret data" into their broadcasts, and that the authorities would take steps to ensure it doesn't happen again.

But some observers suspect it was no accident.

The alleged TV snafu followed an escalation of bellicose rhetoric from the Kremlin.

Relations between Russia and the West, already at Cold War levels over Moscow's interference in Ukraine, have been further strained by Russia's dramatic new role in the civil war in Syria, where it launched air strikes targeting foes of longtime Moscow ally Bashar al-Assad in late September.

The document shown on NTV and First Channel was filmed during a meeting between Putin and Russian military officials in the Black Sea resort of Sochi on November 10.

Its matter-of-fact talk of nuclear Armageddon on "enemy" territory echoed remarks last year by a top presenter on another state channel, Rossia.

"Russia is the only country in the world that is realistically capable of turning the United States into radioactive ash," Dmitry Kiselyov said on his weekly current affairs show in March 2014, a few months after Putin named him to head state news media company Rossia Segodnya:

Lately, Putin himself has not been shy about reminding the West and the world of Russia's nuclear might.

As tensions with the West escalated over Ukraine, Putin mentioned in August 2014 that Russia was a leading nuclear power and advised potential enemies: "It's best not to mess with us."

An Accident?

The rhetoric has not gone unnoticed in the United States.

U.S. Defense Secretary Ash Carter said on November 7 that "Moscow’s nuclear saber-rattling raises questions about Russian leaders’ commitment to strategic stability, their respect for norms against the use of nuclear weapons, and whether they respect the profound caution nuclear-age leaders showed with regard to the brandishing of nuclear weapons."

Pavel Podvig, the author of a blog called Russian Forces, says it's unclear whether the broadcasts showing the document were a security slip or an intentional piece of propaganda.

The fact the video was quickly pulled by the broadcasters suggests it was a mistake, Podvig says. "So, maybe Moscow decided that the leak would not be such a big deal. Still, they would have probably preferred to keep some details out of it," he writes.

But Pavel Felgenhauer, a Russian military analyst, told the Washington Free Beacon newspaper that the "disclosure could have been deliberate." "Without knowing [the weapon exists] there is no deterrence," he said.

Going Nuclear

According to the document, the drone would be launched from two new models of submarines that Russia has started producing over the past three years. It said the drone would reportedly have a maximum range of 5,400 nautical miles (10,000 kilometers) while traveling at a depth of 1,000 meters.

According to Bill Gertz, a military analyst writing for the Washington Free Beacon, the Pentagon was already aware that Russia is developing a drone submarine capable of carrying a nuclear warhead to be used to attack harbors and coasts.

At the meeting in Sochi, Putin said -- as he has several times in the past decade -- that Russia was building weapons designed to penetrate missile shields. He reiterated the Russian accusation that the purpose of a missile defense system the United States is building in Europe is to undermine Russia's security, a charge Washington denies.

"Their true aim is to neutralize the strategic nuclear potential of other nuclear countries...especially our country," Putin was quoted as saying by the state-run TASS news agency.

Putin also said Russia was developing antiballistic-missile-defense systems, but will at first "work on strike systems able to overcome any missile defense system."

A report by the U.S. Congressional Research Service in 2014 said Russia "seems to have increased its reliance on nuclear weapons in its national security concept."